The present invention relates to the magnetic inspection of magnetizable articles and, in particular, to a means for automatically inducing a magnetic field in an elongated metallic workpiece after which the workpiece is dusted with magnetic powder in order to locate defects therein by noting the orientation of the particles on the workpiece surface.
As is well known, if an article consisting of a magnetizable material is subjected to the action of a magnetizing force, lines of magnetic flux are set up in such an article. The paths taken by these lines of flux are in large part determined by both the degree of continuity and the homogeneity of the article. When discontinuities, cracks, flaws or inhomogeneities of any kind are present in a magnetized article, the lines of flux present therein are distorted by such defects. Accordingly, as is also known, if finely divided magnetic particles are deposited on the surface of a magnetized article containing a defect, the particles will, due to the stray lines of flux, be attracted predominantly to the surface of the article immediately above the defect, thus indicating the location of the defect.
This magnetic particle method of defect detection may be utilized as either a primary or secondary workpiece inspection means. When used as the primary inspection system, the magnetizing and inspection operations will often occur directly in the flow path of the manufacture of an article. When used as the secondary inspection system, the magnetic particle inspection will customarily occur following the primary inspection of the workpiece. It is contemplated that such a primary inspection may be accomplished by, e.g., a Non-Destructive Inspection (NDI) unit. Such a NDI unit may inspect the article by means of eddy currents induced in the article. When a defect is detected in the workpiece by the NDI unit, the work is automatically paint sprayed on the surface in the area of the defect. While most defects on the surface can be visually pin-pointed with the aid of the paint spray marks, certain defects are not visible and necessitate further demarcation. In such an instance, a secondary, magnetic particle inspection means is useful, particularly in the embodiment provided herein.
As is apparent from the previous description of the process of magnetic particle flaw detection, the critical and most difficult step in the process is the magnetization of the article. Presently, many facilities effect the magnetization of the workpiece by the time-consuming operation of manually affixing electrical cables to the ends of the workpiece and passing a high amperage electrical current therethrough. Obviously, this is a most dangerous method of magnetization due to the direct human contact with the electrical current source.
Various apparatuses for accomplishing the magnetization of elongated articles have been developed. For example, the apparatuses disclosed in U.S. Pat. Nos. 3,271,663 and 2,990,512 issued to Gewartowski, et al, are directed to magnetic inspection means for billets. Each of these devices accomplishes the magnetization of the billet by a magnetizing means that abuts the ends of the billet. As such, the apparatuses of U.S. Pat. Nos. 3,271,663 and 2,990,512 require the transverse movement of the workpiece out of a straight-line flow path in order to accomplish the magnetization thereof. In fact, no known prior devices have accomplished the magnetization of an elongated workpiece automatically and without necessitating a deviation in the original manufacturing flow path of the work.
The subject invention is directed toward an improved means for rapidly and automatically magnetizing a workpiece which is to be inspected by the magnetic particle inspection method, without necessitating a deviation in the normal straight-line flow path of the workpiece through a manufacturing facility.